1. Field of the Invention
This invention relates to a sheet feeding mechanism and more particularly to a sheet feeding mechanism having a sheet guide assembly for delivering freshly printed sheets from the last printing unit of the press to a pile of sheets without smearing the ink.
2. Description of the Prior Art
In delivering freshly printed sheets from the last printing unit of a printing press to a pile it is essential that the damp sheet be maintained out of contact with a solid surface during the delivery to prevent smearing of the ink. Smearing of the ink commonly occurs on the underside of the sheet when the sheet comes in contact with any of the guide elements that serve to guide the sheet along the path from the last printing unit to the pile. The guide elements are necessary to assure that the freshly printed sheets transported by the gripper mechanisms secured to rotating chains be deposited in proper register on the pile. In order to accommodate variations of sheet length, the guide elements must maintain the movement of the sheets along a directed path and over suction devices. For this reason to meet the variations in the sheet length the guide elements and the suction devices are adjustable in the direction of the sheet movement, i.e., toward and away from the pile.
It is known to direct the movement of the freshly printed sheets along a prescribed path by drive elements such as strings tensioned by weights, tail wheels, slim rods, bands or the like. However, inherent in these types of guide elements is the disadvantage that the printed sheet comes in contact with the guide elements and is therefore smeared before it has had an opportunity to dry. Furthermore, adjustments to these guide elements to accommodate a change in the sheet length is time consuming necessitating stopping of the printing process. Because the above known types of guide elements are effective only linearly wrinkling and creasing of the sheets is common requiring stopping the press in order to make the necessary correction.
There is a need for a sheet delivery mechanism where the printed sheets are taken from the last printing unit by gripper mechanisms that are rotated in a direction from the printing unit to a pile of sheets and where along the path of delivery the freshly printed sheets are maintained from contact with a rigid surface to prevent smearing and are also moved along a path which is adjustable in length to accommodate a variation in length of the sheet being delivered.